There was a strong effect of LW exposure: 57% of those in the top third chose Drug A vs. only 44% of those in the bottom third.

I think this might just be due to the fact that the meme that “time is money” has been repeatedly expounded on LW, rather than long-time LWers are less prone to the decoy effect. All the rot13ed discussions about that question immediately identified Drug C as a decoy and focused on whether a low-income person should be willing to pay $12.50 to be spared a three-hour headache, with a sizeable minority arguing that they shouldn't. I'd look at the income and country of people who chose each drug -- I guess the main effect is what each responded took “low income” to mean.